Equimolar concentrations of 4-phenylsulfonyltrifluoromethanesulfono-o-toluidide (hereafter referred to as MBR-8251), S-ethyl dipropylthiocarbamate (EPTC), and 2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide (alachlor) were compared using a quartz gravel nutrient culture method for detecting toxicity to yellow nutsedge (Cyperus esculentus L.), okra (Hibiscus esculentus L.), cabbage (Brassica oleracia var. captata L.), cucumber (Cucumis sativus L.), and flax (Linum ustitatissimum L.). MBR-8251 was more active on yellow nutsedge than EPTC or alachlor, and MBR-8251 treated nutlets were controlled for a longer period. In general, crops were more tolerant of MBR-8251. Field studies comparing the effectiveness of MBR-8251 to EPTC, S-propyl dipropylthiocarbamate (vernolate), 2-chloro-4-(ethylamino)-6-isopropylamino-s-triazine (atrazine), 3-isopropyl-2,1,3-benzothiazinone-(4)-2,2-dioxide-6,7,8 (BAS-3510), alachlor, and 2-chloro-N-(ethoxymethyl)-6′-ethyl-o-acetotoluidide (MON-097) indicated that after 10 weeks yellow nutsedge control was excellent with MBR-8251, MON-097, and alachlor.

Old-growth forest in Indiana consists of a few remnant stands in a fragmented agricultural landscape. Old-growth stands can differ substantially from more recently disturbed stands in species composition and may be less susceptible to invasion by exotic plant species. Herbaceous species were sampled in quadrats placed in a repeating pattern along two perpendicular transects in six Old-growth stands in Indiana in spring and summer of 2005. Transects extended from forest edges to the center of each stand. Woody exotic species were sampled in 10-m-wide belts centered on each transect during the summer sampling run. Herbaceous exotic species were a minor component of the understory community in all stands and accounted for less than 1% of total herbaceous cover in all six stands. Exotic woody species generally followed a similar pattern. Four sites contained no more than two woody exotic species, and these were encountered at relatively low frequencies and densities. However, European privet and multiflora rose were present in 27 and 48% of quadrats in one stand, respectively. Thus, although both herbaceous and woody exotic species were relatively rare, heavy infestations of woody exotic species are possible. This suggests that, for some Old-growth sites, exotic species can overcome both local and landscape factors that limit their abundance.

Sicklepod is a competitive and prolific weed that emerges throughout the crop season. Glyphosate applications to flowering sicklepod greatly reduce seed production, but there is limited information on glyphosate translocation in flowering weeds. Therefore, a laboratory study was conducted to document the absorption and translocation of 14C-glyhosate in flowering sicklepod. Flowering sicklepod plants were treated with a 14C-glyphosate solution, and 14C-glyphosate absorption and translocation was quantified by scintillation spectrometry. Absorption and translocation of 14C-glyphosate in flowering sicklepod were similar for both 0.21 and 0.42 kg ae ha−1 glyphosate. Although the treated leaflets retained approximately 50% of the recovered 14C-glyphosate, movement of the herbicide was both acropetal and basipetal, with the highest 14C-glyphosate concentrations in the shoot below the treated leaf and the roots. By 96 h after treatment, sicklepod buds and flowers had abscised, but analysis of the structures revealed accumulation of 2% of the recovered 14C-glyphosate. Based on results of the study, effects of glyphosate accumulation in buds and flowers combined with plant stress associated with the primary and secondary effects of glyphosate result in bud and flower abscission, drastically reducing sicklepod seed production.

Two overhead applications of monosodium methanearsonate (MSMA) at either 4 + 4 or 4 + 2.5 lb/A were required for effective postemergence control of rhizome johnsongrass (Sorghum halepense (L.) Pers.) in ratoon sugarcane (hybrids of the genus Saccharum). Two applications of MSMA in the spring controlled 95% of the johnsongrass, whereas two applications of 2,2-dichloropropionic acid (dalapon) at 4.5 lb/A, the standard treatment, controlled only 70%. In heavily infested fields, sugarcane treated with MSMA also outyielded sugarcane treated with dalapon. Sugarcane tolerated MSMA applied before June; the yield of weed-free sugarcane treated with MSMA was not significantly less than that of the untreated control. However, most MSMA treatments, particularly those applied in late spring, caused temporary leaf chlorosis and stunting. Sugarcane sprayed with MSMA before June generally contained no more arsenic in the juice and bagasse at harvest than untreated sugarcane. Application of MSMA in June or August increased the arsenic content, and resulted in concentrations up to 0.45 ppm in juice, and up to 1.68 ppm in bagasse.

Injury to navy bean (Phaseolus vulgaris L.) from EPTC (S-ethyl dipropylthiocarbamate) was investigated as a function of soil moisture, planting depth, soil compaction, temperature, available nitrogen, and seed quality. Experiments in the greenhouse and growth chamber showed that both high and low moisture stress increased injury. Deep planting increased the injury from high rates of EPTC. Soil compaction alone reduced plant growth. In combination with EPTC at 4.5 kg/ha, further growth reduction was observed. Ambient temperature did not alter susceptibility to EPTC. Stimulation of growth by nitrogen as measured by increased fresh weight was inhibited by EPTC. Field and greenhouse studies showed that EPTC injury was greater to mechanically damaged seed than non-damaged seed.

The possibility of using the fungus Bipolaris sacchari as a bioherbicide to suppress cogongrass and to allow the establishment of bahiagrass in cogongrass–bahiagrass mixed plantings was investigated under greenhouse conditions. The bioherbicide was prepared by mixing B. sacchari spore suspension containing 105 spores ml−1 with an oil emulsion composed of 16% horticultural oil plus 10% light mineral oil and 74% sterile water. The bioherbicide caused severe foliar blight in cogongrass and slight phytotoxic damage on bahiagrass. In the first experiment, the bioherbicide reduced cogongrass biomass without affecting bahiagrass biomass. In the second experiment, the bioherbicide caused a 64% reduction in fresh weight, a 74% reduction in the number of rhizomes, and a 47% reduction in the height of cogongrass. The latter experiment also showed an increase in bahiagrass fresh weight in the presence of cogongrass when the bioherbicide was applied. This study indicates the potential of combining bioherbicide application with competition from a desirable grass species as a strategy for the integrated management of cogongrass.

Potassium azide (KN3) was shown to have potential use as a soil fumigant based on the evidence that azide killed dormant seeds in laboratory and field experiments. Volatility was an important factor in the dissipation of KN3; an acid environment greatly increased volatility probably due to rapid conversion to HN3, whereas soil type exerted little influence on vapor loss. Increasing the soil moisture decreased volatility due to water solubility of NH3. KN3 was leachable and weakly adsorbed in various soil types and at different pH levels. From experiments using stoppered flasks to exclude volatility, it was concluded that the dissipation of KN3 was a chemical phenomenon accelerated by elevated temperatures. KN3 dissipated rapidly from an acid soil whether autoclaved or non-autoclaved; however, alkaline soils prevented dissipation of KN3. Apparently, KN3 is converted to HN3 before it is decomposed. Diffusion within the soil was restricted and occurred only in an acid soil. Covering the soil with plastic immediately after application reduced volatility and increased the biological activity of KN3.

Lateral roots of a clone of field bindweed (Convolvulus arvensis L.) were dug each month for 12 months, cut into 6-cm long sections and grown in the dark on moist paper at 23 C to determine if regeneration varies seasonally. New shoots and roots were measured after 8, 11, and 14 days. After 14 days, 69% to 98% of the sections had produced shoots. The mean number of shoots per section was greatest in April (6.4) and least in November (2.0). The monthly mean shoot length ranged from 24 to 43 mm. Although most sections produced shoots, very few produced roots. In May, 31% of the sections grew roots, but only 2% to 16% had new root growth in the other months. For the test period, 83% of the sections produced shoots and only 10% produced roots.

Pesticide retention by eight inorganic soil amendments, the majority of which are used in turf, was evaluated using a laboratory-based technique with radiolabeled pesticides. Amendments evaluated were derived from various naturally-occurring deposits of zeolites, diatomaceous earths, and fired clays and are intended to provide long-lived, stable, and uniformly sized particles that can contribute favorable water- and nutrient-retention properties to the root zone. Sand, sedge peat, and a Marvyn loamy sand soil (Ap horizon) were included for comparative purposes. Pesticides evaluated included the herbicides imazaquin and oxadiazon and the fungicide/herbicide fenarimol. Pesticide retention was evaluated with a soil solution technique. Amendments evaluated had considerable variation in cation exchange capacity (CEC), effective CEC (ECEC), surface area (SA), and field capacity with lesser variation in particle size distribution and particle density. Scanning electron microscopy revealed that surface texture was variable but frequently rough and porous. Pesticide retention was also variable but generally more than that of sand and frequently equivalent to sedge peat. Only with fenarimol and amendments that had been Ca+2-saturated could retention be correlated with any of the individual physical or chemical parameters that are generally assumed to govern pesticide adsorption, which in this case were CEC and SA. Imazaquin retention by unaltered amendments was correlated only with the products of SA and CEC, and SA and ECEC. Retention of both oxadiazon and fenarimol by unaltered amendments could not be correlated with any individual physical and chemical parameters or products thereof. Pesticide retention by these amendments is probably the cumulative sum of both true adsorption and physical entrapment.

The phytotoxicities of soil-incorporated 2,6-dichlorobenzonitrile [dichlobenil] and 2,6-dichlorothiobenzamide [hereinafter referred to as SD-7961] were compared in five soils in the greenhouse. Dichlobenil and SD-7961 were about equally toxic to snap beans (Phaseolus vulgarus L., var. Black Valentine) in each of the five soils. The herbicides were more toxic in Christiana loam than in the other four soils. Phytotoxic residues of both herbicides disappeared most rapidly from Hagerstown silty clay loam and Christiana loam and least rapidly from Sharkey clay. Gas chromatographic analyses of soil extracts confirmed that dichlobenil was most persistent in the clay. Small amounts (0.14 ppmw or less) of 2,6-dichlorobenzoic acid [hereinafter referred to as 2,6-DBA] were detected in soil from greenhouse pot cultures about 9 months after incorporation of dichlobenil. In a field experiment at Beltsville, Maryland, residues of dichlobenil persisted from one season to the next but did not build up in soil sprayed annually for 3 years with 4 or 8 lb/A. Some movement from the surface 6 in into the 6 to 12-in zone occurred on plots sprayed 2 years in succession with 8 lb/A or once with 40 lb/A. Rapid loss of dichlobenil occurred during summer months. When the concentration of dichlobenil on the 40-lb/A plots dropped to about 10%, subsequent loss occurred at a very slow rate.

Adsorption and desorption characteristics of fluridone (1-methyl-3-phenyl-5-[3-txifluoromethyl)phenyl]-4-(1H)-pyridinone} on prepared clays and organic matter were studied in unbuffered and buffered aqueous solutions. In unbuffered aqueous solution the adsorption of fluridone decreased in the order: H-saturated organic matter (H-OM) > Ca-saturated montmorillonite (Ca-mont) > Ca-saturated organic matter (Ca-OM) > kaolinite. Based on the chemistry of fluridone, the nature of the adsorbent, and previously reported studies, the major adsorption mechanisms appear to be pH-dependent adsorption of protonated fluridone and direct protonation of the herbicide at acidic surfaces, supplemented by physical adsorption forces such as van der Waals attractions and charge transfer bonds. The adsorption of fluridone on Norfolk sand (Typic Paleudult; fine-loamy, siliceous, thermic), unmodified (CK), or amended with montmorillonite (HC) or organic matter (HM) at pH 4.0, 5.2, and 7.0 was also studied. Over all adsorption was greatest on HC soil, least on CK soil, and intermediate on the HM soil. In each system adsorption was inversely related to pH. These results were interpreted by comparison with adsorption observed on prepared clay minerals and organic matter.

Amicarbazone controls annual bluegrass in cool-season turfgrasses but physiological effects that influence selectivity have received limited investigation. The objective of this research was to evaluate uptake, translocation, and metabolism of amicarbazone in these species. Annual bluegrass, creeping bentgrass, and tall fescue required < 3, 56, and 35 h to reach 50% foliar absorption, respectively. At 72 h after treatment (HAT), annual bluegrass and creeping bentgrass translocated 73 and 70% of root-absorbed 14C to shoots, respectively, while tall fescue only distributed 55%. Annual bluegrass recovered ≈ 50% more root-absorbed 14C in shoots than creeping bentgrass and tall fescue. Creeping bentgrass and tall fescue metabolism of amicarbazone was ≈ 2-fold greater than annual bluegrass from 1 to 7 d after treatment (DAT). Results suggest greater absorption, more distribution, and less metabolism of amicarbazone in annual bluegrass, compared to creeping bentgrass and tall fescue, could be attributed to selectivity of POST applications.

Weed emergence models require biological parameters such as base temperature for germination, determination of which is costly and time-consuming. Transferability of these parameters across different populations may therefore represent one of the main constraints for the development and practical use of emergence models at a large scale. A collaborative project was undertaken to assess the interpopulation variability of base temperature for germination in different European populations of velvetleaf and jimsonweed and evaluate possible applicative consequences in terms of weed control. Seeds were collected in Italy, Portugal, and Spain, and each population was then sown in every country, obtaining nine seed batches named as experimental lots. Base temperature for germination was estimated for each experimental lot to calculate lot-specific accumulation of growing degree days (GDD) under three dissimilar climatic scenarios. Threshold date (TD50) was calculated as the date when GDD accumulation of a given experimental lot surpassed the values corresponding to 50% of cumulative field emergence of seedlings. GDD accumulation and TD50 were then used as indicators to identify differences among experimental lots within each climatic scenario. No significant differences were detected among base temperatures estimated for velvetleaf experimental lots or among their patterns of accumulation of GDD and TD50 values within climatic scenarios. Each value of base temperature determined for a single experimental lot could therefore be adopted to model germination for all the lots regardless of the population of origin or cultivation site. In contrast, the population of origin affected the base temperature for jimsonweed, with significantly higher values for experimental lots of the Portuguese population. From an applicative perspective, differences among patterns of accumulation of GDD and TD50 of several experimental lots within each climatic scenario suggest the need to use population-specific values as base temperature for germination and emergence modeling of jimsonweed.

Ryegrass (Lolium spp.) is a troublesome weed in major wheat (Triticum aestivum L.) production regions in the United States. High diversity and adaptive potential are known to contribute to its success as a weed species and also create difficulties in correct species identification in fields. The objective of this research was to characterize diversity for 16 different morphological traits among 56 Lolium populations collected from wheat production fields across the Texas Blackland Prairies region and identify Lolium species based on taxonomic characteristics. Populations were highly diverse (both at inter- and intrapopulation levels) for the traits studied, and a taxonomic comparison with USDA-GRIN reference samples revealed that all the populations were variants of Italian ryegrass [Lolium perenne L. ssp. multiflorum (Lam.) Husnot] with a few offtypes of perennial ryegrass (Lolium perenne L.) or probable hybrids between the two species. Hierarchical clustering grouped the populations into six clusters based on their similarities for the morphological traits investigated. Principal component analysis showed that the variability for yield traits greatly contributed to the total diversity. Pre-flowering plant height (stage 10 on Feekes scale) was positively correlated with tiller count, shoot biomass, and spike count, but not with total seed count per plant, whereas plant height at maturity (stage 11.3 to 11.4 on Feekes scale) was highly correlated with total seeds per plant. Further, basal node color was positively correlated with plant growth habit, regrowth rate, and leaf color. Leaf blade width was positively correlated with survival to pinoxaden and multiple herbicides, whereas, spike count was negatively correlated with survival to mesosulfuron. The high levels of intra- as well as interpopulation variability documented in this study indicate the potential of this species to rapidly adapt to herbicides and emphasize the need for implementing diverse management tactics, including the integration of harvest weed seed control.

Traditional breeding has been used to develop grain sorghum germplasm that is tolerant to acetolactate synthase (ALS)-inhibiting herbicides (Inzen Technology, DuPont). Inzen sorghum carries a double mutation in the ALS gene (Val560Ile and Trp574Leu), which confers high level of tolerance to ALS-inhibiting herbicides. Overreliance on ALS-inhibiting herbicides for weed control during the 1990s resulted in the evolution of ALS inhibitor–resistant shattercane populations in Nebraska. According to a survey conducted in 2013, ALS inhibitor–resistant weedy Sorghum populations persist in Nebraska. The objectives of this research were to determine whether the ALS mutations present in Inzen sorghum were present in the ALS inhibitor–resistant shattercane and johnsongrass populations detected in Nebraska and northern Kansas, and whether these populations evolved ALS resistance independently. Primers specific to the Val560 and Trp574 region of the ALS gene were used to screen the populations with PCR. The Trp574Leu mutation was present in one ALS inhibitor–resistant johnsongrass population. The Val560Ile was detected in three ALS inhibitor–resistant shattercane, one susceptible shattercane, one ALS inhibitor–resistant johnsongrass, and one susceptible johnsongrass population. Moreover, Val560Ile was present in resistant and/or susceptible individuals within johnsongrass and shattercane populations that were segregating for ALS resistance, indicating that by itself the Val560Ile mutation does not confer resistance to ALS-inhibiting herbicides. None of the populations presented both mutations simultaneously, as does Inzen sorghum. A shattercane population containing the Ser653Thr mutation was also detected. This research indicates that the ALS mutations present in Inzen sorghum already exist individually in weedy sorghum populations. Moreover, our results present strong evidence that ALS resistance in these populations evolved independently. Thus, widespread overreliance on ALS-inhibiting herbicides prior to adoption of glyphosate-tolerant crops in the 1990s exerted sufficient selective pressure on shattercane and johnsongrass populations for resistance to evolve multiple times in the Midwest. Finally, a survey of the 5′ portion of the ALS gene in more diverse wild and weedy Sorghum species was hampered by limited coverage in genomic resequencing surveys, suggesting that refined PCR-based methods will be needed to assess SNP variation in this gene region, which includes the Ala122, Pro197, and Ala205 codons known to confer ALS resistance in other species.

Protoporphyrinogen oxidase (PPO)-inhibiting herbicides remain an important and useful chemistry 60 yr after their first introduction. In this review, based on topics introduced at the Weed Science Society of America 2021 symposium titled “A History, Overview, and Plan of Action on PPO Inhibiting Herbicides,” we discuss the current state of PPO-inhibiting herbicides. Renewed interest in the PPO-inhibiting herbicides in recent years, due to increased use and increased cases of resistance, has led to refinements in knowledge regarding the mechanism of action of PPO inhibitors. Herein we discuss the importance of the two isoforms of PPO in plants, compile a current knowledge of target-site resistance mechanisms, examine non–target site resistance cases, and review crop selectivity mechanisms. Consistent and reproducible greenhouse screening and target-site mutation assays are necessary to effectively study and compare PPO-inhibitor resistance cases. To this end, we cover best practices in screening to accurately identify resistance ratios and properly interpret common screens for point mutations. The future of effective and sustainable PPO-inhibitor use relies on development of new chemistries that maintain activity on resistant biotypes and the promotion of responsible stewardship of PPO inhibitors both new and old. We present the biorational design of the new PPO inhibitor trifludimoxazin to highlight the future of PPO-inhibitor development and discuss the elements of sustainable weed control programs using PPO inhibitors, as well as how responsible stewardship can be incentivized. The sustained use of PPO inhibitors in future agriculture relies on the effective and timely communication from mode of action and resistance research to agronomists, Extension workers, and farmers.

Growth habit is an important determinant of competitive ability in legume crops. Erect ‘Iron-Clay’ (IC), semi-erect ‘IT89KD-288’ (288), and prostrate ‘UCR 779’ (779) cowpea genotypes were planted with four densities of common sunflower or common purslane to determine which cowpea growth habit is more competitive to these weeds having markedly different statures. Both sunflower and purslane reduced cowpea relative growth rate (RGR) but at different phases of the growing season. Low-growing purslane had an effect in the earlier part of the season, and sunflower decreased cowpea RGR in the middle of growing season. RGR of genotype IC was the least affected and genotype 779 the most reduced by sunflower. Cowpea apparently compensated for early season purslane competition by increasing RGR after purslane flowering, with RGR for the IC genotype increasing the most and 779 increasing the least. All cowpea genotypes caused a similar reduction in sunflower biomass accumulation; but purslane biomass was most reduced by genotype IC and least affected by genotype 288. Erect genotype IC is more competitive due to its taller stature, greater height growth rate, and higher position of maximal leaf area density, despite a lower photosynthetic rate and light use efficiency than the other cowpea genotypes. Our results suggest that erect cowpea growth habit may be generally more competitive with weeds compared to semi-erect or prostrate growth habit.

The tolerances of wheat and wild buckwheat (Polygonum convolvulus) to various rates of 2-methoxy-3,6-dichlorobenzoic acid (dicamba) were determined under field conditions and supplemented by studies with wheat in the growth chamber. Wheat height and yield were inversely proportional to rate, but response to various rates was dependent on stage of growth at application. Greatest reductions in wheat height and yield resulted from treatment at the late tiller and boot stages, respectively. The weight per 100 wheat seeds was increased from treatment at the boot and flower stages but was decreased at the early tiller stage.

The ratio of peduncle length: length of the flag leaf-sheath was decreased most from 24 oz/A applied preemergence and 12 oz/A applied at the late tiller stage.

Growth rate of wheat was decreased for a 2-week period after treatment. Excellent kill of wild buckwheat was observed from all rates applied through the 12- to 15-leaf stage of growth.

Application of 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) generally reduced dry weight of tops and roots of corn and Pinus radiata seedlings. Simazine always increased top-root ratios of corn but generally decreased those of pine seedlings. Simazine increased significantly the uptake of N by corn in all soils; of Mg and P in limed, and of K in acidified soils. Aluminum sulfate decreased injury from simazine. Lime at 3 tons per acre mixed into the soil exerted a synergistic effect on the activity of 12 pounds per acre of simazine and killed all pine seedlings in the 7th or 8th week after sowing. The death of the seedlings was. caused by excess calcium ions and not by pH.

The influence of temperature, light, solution pH, water stress, salt stress, and burial depth on seed germination and seedling emergence of catchweed bedstraw and the sensitivity of that weed to commonly available herbicides in China were studied in laboratory and greenhouse. Germination occurred at day/night temperatures from 5/0 C to 30/25 C, with optimum germination at 15/10 C. Catchweed bedstraw germinated equally well under a 12-h photoperiod and continuous darkness; however, a 24-h photoperiod inhibited seed germination. Catchweed bedstraw seed is moderately sensitive to osmotic potential and salt stress, with 15 and 3% germination rates at an osmotic potential of −0.5 Mpa and salinity level of 120 mM, respectively. Maximum seed germination was observed in near neutral pH; germination was greater than 80% over a broad pH range from 5 to 8. Seedling emergence of the seeds buried at a depth of 1 cm was higher (74%) than those placed on the soil surface (20%), but declined with burial depth increasing. Few (10%) seedlings emerged when seeds were placed at a depth of 5 cm. Bensulfuron-methyl, and ethametsulfuron-methyl applied PRE and tribenuron-methyl, fluroxypyr, and florasulam applied POST can be used to provide greater than 80% control of catchweed bedstraw. The results of this study have contributed to more complete understanding of the germination and emergence of catchweed bedstraw.